[gtobird]

Just wanted to add a note to this. I have two blower housings. One of them is original to the car and the other is a used GM housing and both of them are perfectly clean with nothing on the flange face that mates with the firewall. I found that when I place them face down on a table, there is a small gap between the flange face and the table in the same location as when they are on the car, though the gap is only about 1/16" vs 1/8" when on the car